Southwest Anthony Henday Drive Noise Study 1
Introduction to Sound 2
Decibel Scale • Noise is measured using a Decibel (dB) Scale • The Decibel Scale is a base-10 logarithm scale (similar to Richter Scale) – Change of 1-2 dB - threshold for subjective change – Change of 3 dB - barely perceptible – Change of 5 dB - strongly perceptible – Change of 10 dB - considered twice as loud 3
Decibel Scale 4
A-Weighting Scale (dBA) • An “A - Weighting” scale ( dBA) is being used to measure sound in the SW AHD noise study – A-weighting matches human hearing • Human hearing is not linear at different frequencies (i.e. pitch) • Human hearing reduces the volume of both low and high frequency (pitch) sounds compared to middle frequency sounds 5
Fluctuating Sounds Energy Equivalent Sound Level (L eq ) over a 24-hour period L eq 24 = 57.5 dBA 6
Energy Equivalent Sound Level • Over time, sound is measured using the Energy Equivalent Sound Level (L eq ) – Takes into account noise fluctuations – A short burst of loud noise is perceived to be as annoying to the average person as sustained noise at a lower level (i.e., loud air brakes for a short time versus continuous, low- level traffic noise) – One number represents all this data over a given time period – Uses Logarithmic Average of sound (not arithmetic) 7
Energy Equivalent Sound Level • The SW AHD noise study uses a 24-hour time period for the Energy Equivalent Sound Level (L eq ) – Sound is continuously measured by the noise monitor and the L eq is logged every 15 seconds for the entire 24- hours. – The L eq is determined largely by louder sound levels. – The purpose of this method is to reflect the way that people respond to sound. 8
Factors that Affect Noise • Certain conditions affect how noise travels and is perceived – Wind – Temperature – Topography – Ground cover • These conditions influence how and when noise monitoring can take place 9
Factors that Affect Noise - Wind • Single biggest reason for day-to-day fluctuations in urban noise • Decreased noise level upwind, increased noise level downwind • The difference between sound upwind/downwind can be +10 dBA Wind Source Shadow Zone 10
Factors that Affect Noise - Temperature • Normal gradient (i.e. colder temp. at higher elevation) generally has neutral effect on sound • Temperature inversion (i.e. warmer temp. at higher elevation) can reflect sound back towards ground • Difference can be +10 dBA • Temperature inversion occurs when wind is calm 11
Factors that Affect Noise - Temperature 12
Factors that Affect Sound Travel • Rain – Falling rain (or snow) has little effect on sound travel – Wet road surface has different sound “quality” than dry • Topography – Hills can provide sound attenuation – Valleys can provide sound amplification • Ground Cover – Grass, grain crops, foliage can absorb sound – Snow cover can absorb or reflect sound 13
Traffic Noise 14
Sources • Dominated by tire noise at speeds greater than about 50 km/h • Engine noise (from front grill and reflections off road) • Exhaust noise (higher up for large trucks and busses) • Turbulent wind noise 15
Variables • Road surface type and conditions • Vehicle type and condition (passenger vehicles, trucks, buses and motorcycles) • Tire configuration • Number of vehicles, vehicle speeds • Engine load 16
Levels • Distance reduces noise — the further you are away from the noise, the quieter it is • 2x traffic volume results in a 3 dBA increase (barely subjectively noticeable) – Double the traffic volume does not result in double the noise • 10x traffic volume results in a 10 dBA increase (subjectively twice as loud) 17
Current Noise Study 18
Policy Alberta Transportation Noise Attenuation Guidelines for Provincial Highways: “For construction or improvements of highways through cities and other urban areas, Alberta Transportation will adopt a noise level of 65 dBA L eq 24 measured 1.2 m above ground level and 2 m inside the property line (outside the highway right-of-way). The measurements should be adjusted to the 10-year planning horizon , as a threshold to consider noise mitigation measures.” 19
Policy • Noise levels are measured objectively (1.2 m above ground level and 2 m inside the property line) to ensure all are treated fairly • Alberta Transportation’s noise policy is similar to that of the City of Edmonton 20
Noise Study Purpose • Initiated by Alberta Transportation (AT) based on Ministerial commitment to conduct the study in 2016, prior to the original 2018 timeline. • Current noise levels will be compared to 2007 and 2013 noise monitoring results, and against AT’s noise level guidelines. 21
Noise Monitoring • Where – 13 locations throughout study area – Same locations as 2007 and 2013 • When – 24-hour monitoring period – Downwind conditions – Four separate monitoring periods to cover all locations under appropriate wind conditions 22
Stony Plain Road Study Area 87 Avenue Whitemud Drive 62 Avenue = Noise Monitor Lessard Road Terwillegar Calgary Road Trail Rabbit Hill Road 23 111 Street
Current Noise Study: Monitoring • How – dBA and frequency data recorded every 15 seconds – Simultaneous digital audio recording for “isolation” analysis – Portable weather monitoring station obtains accurate local meteorological conditions • Why – For the calibration and verification of the noise model 24
Modelling • Computer noise model of entire study area considers: – Traffic on SW AHD, as well as all intersecting Edmonton roads and interchanges – Elevation contours – Residential property lines – Residential and commercial structures • Noise levels are calculated at 1.2 m elevation, 2 m inside property line • Colour noise maps are calculated for entire study area • Sensitivity analysis is created to account for fluctuations in traffic volumes, heavy trucks, speed 25
Noise Study Timeline • Noise monitoring began a few weeks ago, however, due to construction in the area, monitoring at all locations could not be completed. • Next spring (as soon as weather permits) monitoring will resume at all locations. Sites completed in 2016 will be redone to ensure a standardized baseline. • Monitoring will take approximately 6 weeks to complete. • Following monitoring, the noise modeling and analysis will be completed. The final report is expected in late summer. 26
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